This application is based on Japanese Patent Application Nos. 2000-95249 and 2000-368344, filed on Mar. 29, 2000 and Dec. 4, 2000, respectively, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical or taking lens device. More specifically, the present invention relates to a taking lens device that optically takes in an image of a subject through an optical system and then outputs the image as an electrical signal by means of an image sensor, for example a taking lens device that is used as a main component of a digital still camera, a digital video camera, or a camera that is incorporated in, or externally fitted to a device such as a digital video unit, a personal computer, a mobile computer, a portable telephone, or a personal digital assistant (PDA). The present invention relates particularly to a taking lens device which is provided with a compact, high-zoom-ratio zoom lens system.
2. Description of Prior Art
In recent years, as personal computers and other data processing devices have become more and more popular, digital still cameras, digital video cameras, and the like (hereinafter collectively referred to as digital cameras) have been coming into increasingly wide use. Personal users are using these digital cameras as handy devices that permit easy acquisition of image data to be fed to digital devices. As such image data input devices, digital cameras are expected to continue gaining popularity.
In general, the image quality of a digital camera depends on the number of pixels in the solid-state image sensor, such as a CCD (charge-coupled device), which is incorporated therein. Nowadays, many digital cameras, which are designed for general consumers, boast of high resolution of over a million pixels, and are thus approaching silver-halide film cameras in image quality. On the other hand, even in digital cameras designed for general consumers, zoom capability (especially optical zoom capability with minimal image degradation) is desired, and therefore, in recent years, there has been an increasing demand for zoom lenses for digital cameras that offer both a high zoom ratio and high image quality.
However, conventional zoom lenses for digital cameras that offer high image quality over a million pixels are usually built as relatively large lens systems. One way to avoid this inconvenience is to use, as zoom lenses for digital cameras, zoom lenses which were originally designed for lens-shutter cameras in which remarkable miniaturization and zoom ratio enhancement have been achieved in recent years. However, if a zoom lens designed for a lens-shutter camera is used unchanged in a digital camera, it is not possible to make good use of the light-condensing ability of the microlenses disposed on the front surface of the solid-state image sensor. This causes severe unevenness in brightness between a central portion and a peripheral portion of the captured image. The reason is that in a lens-shutter camera, the exit pupil of the taking lens system is located near the image plane, and therefore, off-axial rays exiting from the taking lens system strike the image plane from oblique directions. This can be avoided by locating the exit pupil away from the image plane, but not without making the taking lens system larger.
An object of the present invention is to provide a taking lens device or optical device which is provided with a novel zoom lens system that, despite. being compact, offers both a high zoom ratio and high image quality.
To achieve this object, according to one aspect of the present invention, an optical or taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units which achieves zooming by varying the unit-to-unit distances and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system is comprised of at least, from the object side thereof to an image side thereof, a first lens unit having a negative optical power and a second lens unit having a positive optical power, and the following conditional formulae are fulfilled:
2 less than |f1/fw| less than 4
0.058 less than (tan xcfx89w)2xc3x97fw/TLw less than 0.9
where
f1 represents the focal length of the first lens unit;
fw represents the focal length of the entire optical system at the wide-angle end;
tan xcfx89w represents the half view angle at the wide-angle end; and
TLw represents the total length (the distance from the first vertex to the image plane) at the wide-angle end.
According to another aspect of the present invention, an optical or taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units which achieves zooming by varying the unit-to-unit distances and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system is comprised of at least, from the object side thereof to an image side thereof, a first lens unit having a negative optical power, a second lens unit having a positive optical power, and the following conditional formulae are fulfilled:
2 less than |f1/fw| less than 4
10 less than TLwxc3x97Fnt/(fwxc3x97tan xcfx89w) less than 40
where
f1 represents the focal length of the first lens unit;
fw represents the focal length of the entire optical system at the wide-angle end;
TLw represents the total length (the distance from the first vertex to the image plane) at the wide-angle end;
Fnt represents the f-number at the telephoto end; and
tan xcfx89w represents the half view angle at the wide-angle end.